High-pressure electric discharge device containing mercury, halogen, scandium and samarium

ABSTRACT

A metal arc lamp, which emits all visible colors in the spectrum and has good red rendition, contains a fill including mercury, halogen, scandium and samarium. The lamp is an efficient producer of white light.

United States Patent [50] Field of Search.......

[72] Inventors Frederic Koury Lexington;

John F. Waymouth, Marblehead, Mass. [21] Appl.No 780,117

Nov.29,1968 [45] Patented May4, 1971 [22] Filed [73] Assignee Sylvania Electric Products, Inc.

Primary Examiner-Raymond F. Hossfeld [54] HIGHPRESSURE ELECTRIC DISCHARGE Attorneys-Norman J. OMaIley and James Theodosopoulos DEVICE CONTAINING MERCURY, HALOGEN,

ABSTRACT: A metal are lamp, which emits all visible colors in the spectrum and has good red rendition, contains a fill including mercury, halogen, scandium and samarium. The lamp is an efficient producer of white light.

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PATENIED 1m 4m 3577.029

JOHN F WAYMOUTH FREDERIC KOURY INVENTORS WTW AGENT HIGH-PRESSURE ELECTRIC DISCHARGE DEVICE Y CONTAINING MERCURY, HALOGEN, SCANDIUM AND 'SAMARIUM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to high pressure electric discharge lamps and particularly to those containing atoms of mercury, halogen and light-emitting metals.

2. Description of the Prior Art Rare earth metals have been introduced into the fill of highpressure electn'c discharge lamps to provide a closely spaced, forest of emission lines and, therefore, a light source which emits a continuum of light. over the visible spectrum. US. Pat. No. 3,334,261, issued on Aug. 1, 1967 to'Butler et al., illustrates some useful lamp fills containing rare earth metals.

U..S. Pat. No. 3,407,327, issued on Oct. 22, 1968 to Koury et al., shows a high-pressure electric discharge device containing mercury, halogen, scandium and an alkali metal and which is an efficient producer of white light.

. UMMABX. QF T EINVEFTIPN fill containing the above-mentioned light-emitting metals separately. For example, in a particular lamp containing a fill of mercury, iodine, samarium and scandium, 32,000 to 34,000 lumens were produced. With the same fill, but using only scandium as the light-emitting metal, only 25,000 to 28,000 lumens were produced. And with only samarium, only 20,000 lumens were produced.

Preferably, the samarium and scandium are present in the fill in an atomic ratio of 1:1 respectively, although the ratio may vary from about 1%:1 to 1:2 without substantial detriment to the efficiency and color of the light produced. Preferably, also, the total concentration of samarium plus scandium is about 0.22Xl0 gram atoms per cm. of arc length but may vary from about 4.6x l 0 to l:lXl0 gram atoms per cm. of arc length.

In addition, mercury either as a metal or as an iodide, must be included in the filling of the tube, the quantity of mercury being such as to allow complete vaporization at normal operating temperatures of the are tube and to form a restricted arc therein. To achieve maximum white light emission, certain ratios in the number of iodine atoms to mercury atoms must be maintained and although we prefer a ratio of about 0.45, it is possible to use a ratio between 0.10 to 0.85. It is sometimes advantageous to add 5.25X10 to 6.8)(10 gram atoms per centimeter of arc tube length of an alkali metal, preferably cesium, forming a low vapor pressure iodide, to stabilize the arc and insure at room temperature that there is little or no iodine in the vapor state thereby lessening starting voltages.

BRIEF DESCRIPTION OF THE DRAWING The single FIG. is an elevational view of a high-pressure electric discharge device in accordance with this invention and illustrates the positioning of an arc tube containing a lamp fill within an outer bulbous envelope.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the FIG., an elevational view of a high-pressure electric discharge device is shown. The device such as shown in the drawing comprises an outer vitreous envelope or jacket 2 of generally tubular form having a central bulbous portion 3.

The jacket is provided at its end with a reentrant stem having a press through which extend relatively stiff lead-in wires 6 and 7 connected at their outer ends to the electrical contacts of the usual screw-type base 8 and at their inner ends to the arc tube and the harness.

The are tube is generally made of quartz although other types of high temperature glass may be used, such as alumina glass. Sealed in the arc tube 12 at the opposite ends thereof are main discharge electrodes 15 and 16 which are supported on lead-in wires 4 and 5 respectively. Each main electrode 15 and 16 comprises a core portion which may be a prolongation of the lead-in wires 4 and 5 and may be prepared of a suitable metal such as for example molybdenum or tungsten. The prolongations to these lead-in wires 4 and S are surrounded by molybdenum or tungsten wire helixes.

An auxiliary starting probe or electrode 18, generally prepared of tantalum or tungsten is provided at the base end of the arc tube 12 adjacent the main electrode 16 and comprises an inwardly projecting end of another lead-in wire.

Each of the current lead-in wires described have their ends welded to intermediate foil section of molybdenum which are hermetically sealed within the pinched sealed portions of the arc tube. The foil sections are very thin, for example approximately 0.0008 inch thick and go into tension without rupturing or scaling off when the heated arc tube cools. Relatively short molybdenum wires 23,24 and 35 are welded in the outer ends of the foil and serve to convey current to the various electrodes inside the arc tube 12.

Metal strips 45 and 46 are welded into the lead-in wires 23 and 24 respectively. A resistor 26 is welded to foil strip 45 which in turn is welded to the arc tube harness. The resistor may have a value of for example, 40,000 ohms and serves to limit current to auxiliary electrode 18 during normal starting of the lamp. Metal foil strip 46 is welded directly to stiff leadin wire 7. Lead-in wire 35 is welded at one end to a piece of molybdenum foil sealed in the arc tube 12 which in turn is welded to main electrode 13. Metal foil strip 47 is welded to one end of lead-in wire 35 and at the other end of the harness. The pinched or flattened end portions of the arc tube 12 form a seal which can be of any desired width and can be made by flattening or compressing the ends of the arc tube 12 while they are heated.

The arc tube 12 is provided with a filling of mercury in a quantity such as to vaporize completely when a pressure in the order of one half to several atmospheres is reached during normal lamp operation at temperatures of 450 to 700 C. Particularly we have found that through the addition of certain mercury iodides to the mercury fill, that the quantity of the latter can be reduced to as low as 1.25Xl0 gram atoms per centimeter of arc length and possibly lower; arc length being measured as the distance between opposing tips of the main electrodes 15 and 16. The amount of mercury added can be varied widely as we have indicated, although we prefer to add approximately 2.5X10 to 4.1 l0 gram atoms of mercury per centimeter of arc length. The continuum or white light emission appears to be substantially independent of the amount of mercury metal added and hence the quantity of the latter can be reduced while white light emission is still attained.

As is conventional in the art, a quantity of rare gas such as helium, argon, neon, krypton or xenon at a pressure of about 25 millimeters of mercury is added to facilitate starting. In addition to these materials we have discovered that a mercury iodide, or combination of elemental mercury and elemental iodine, must be added to the arc tube to attain white light emission. Particularly we have discovered that about 0.45 atom of iodine must be added for every atom of mercury irrespective of whether the mercury atoms are derived from the metal or from the mercury compound, although this ratio may be varied in reasonable tolerances between 0.10 to 0.85 atom of iodine per atom of mercury. It is quite important to use anhydrous material in the arc tube since the incorporation of water tends to make the discharge hard to start.

The U-shaped internal wire supporting assembly or are tube harness serves to maintain the-position of the arc tube 12 substantially coaxial'within the envelope 2. To support the arc tube 12 within the envelope, stiff lead-in wire 6 is welded to the base 53 of the harness. Because stiff lead-in wires 6 and 7 are connected to opposite sides of a power line, they must be insulated from each other together with all members associated with each of them. Clamps 56 and 57 hold the arc tube 12 at the end portions and are fixedly attached to legs 54 of the harness. A rod 59 bridges the free ends of the U-shaped support wire 54 and is fixedly attached thereto for imparting stability to the structure. The free ends of the U-shaped wire 54 are also provided with a pair of metal leaf springs 60, frictionally engaging the upper tubular portion of the lamp envelope 2. A heat shield 61 may be disposed beneath the arc tube 12 and above the resistor 26 so as to protect the resistor from excessive heat generated during lamp operation.

As we have stated, for attaining maximum white light emission a ratio of iodine atoms to mercury atoms should be maintained at approximately 0.45. However, white light emission will still be obtained when the ratio is greater or less than 0.45, (within definite limits) but the emission is reduced using such off peak ratios. Since it is difficult, if not impossible, to produce lamps in production lines wherein the ratio of halogen to mercury is exactly 0.45, tolerances are allowed between 0.10 to 0.85 and within such tolerances, reasonably white light emission is still evidenced.

When adding the samarium and scandium, 0.046Xl to 1L1 l0-" gram atoms of total metal per centimeter of arc length should be added. Above this range the metals tend to deposit upon the walls of the arc tube, while below the range nocontinuous spectrum is evidenced. The metals may be added in elemental form or as the corresponding iodides or mixtures thereof.

The fabrication of the envelope, sealing techniques and positioning of the electrodes in the high-pressure electric discharge device according to our invention takes place in a manner quite similar to that known to the art with conventional mercury lamps. And further, the mercury metal may be added to the arc tube' by techniques well known to the art. To

arc tube. Hydrogen is known to affect the starting of mercury lamps adversely but its effect appears to be greater in the lamps prepared according to our invention. The difiiculty with hydrogen appears to be due to the formation of hydrogen iodide which has a much higher vapor pressure than any other iodide present. We believe that for every atom of hydrogen present, that there is an extra atomof iodine in the vapor state. Presence of the iodine in the vapor s'tateincfreases the voltage which must be applied to the lamps for starting. Hence, not only must hydrogen be substantially eliminated from the gases in the fill tube but each and every part going into making up the arc tube must be freed of residual hydrogen impurities. For example, the electrodes should be vacuum baked at 300 to 400 C. for a few hours before their use to eliminate hydrogen which might occur due to processing. Furthermore, care should be exercised when sealing the electrodes into the arc tube to prevent hydrogen-containing, combustion gases from seeping in or becoming absorbed upon the surface.

The pump and fill procedure above described is usually repeated three to four times and then an arc is struck between the electrodes while there is a filling of argon gas. This operation of the arc removes any residual impurities from the electrodes and these contaminants can then be easily drawn from the system when the argon filling is pumped out. We then add approximately 50 milligrams of mercury, 5 milligrams of mercuric iodide, 0.8 milligrams of samarium and 0.25 milli rams of scandlum to an arc ube having an arc length of 45 mi Imeters. The are tube is then filled to atmospheric pressure with argon gas which is slowly leaked out until a pressure of about 23 millimeters of mercury is obtained. Subsequently, the exhaust tubulation is tipped off and the envelope is sealed. Testing of the lamp indicates that a white light emission is evidenced, which emission is in the order of lumens per watt and which has a ClE color rendering index of 85.8.

We claim:

1. A high-pressure arc discharge device comprising: an arc tube having electrodes sealed at either end thereof and a vaporizable fill of a quantity of iodine, mercury, samarium and scandium; said iodine and mercury respectively being present therein at anatomic ratio of O.l0 to 0.85 to said mercury being present in sufficient quantities to be completely vaporized at predetermined operating temperatures of said are tube and to form' a restricted arc therein.

2. The device claim 1 wherein said samarium and said scandium are present in quantities of 4.6X10- to 1.1X10 gram atoms per'centimeter of arc length.

3. The device of claim 2 wherein .the atomic ratio of said samarium to said scandium is respectively between about 

2. The device claim 1 wherein said samarium and said scandium are present in quantities of 4.6 X 10 7 to 1.1 X 10 5 gram atoms per centimeter of arc length.
 3. The device of claim 2 wherein the atomic ratio of said samarium to said scandium is respectively between about 1 1/2 :1 and 1:2.
 4. The device of claim 1 wherein said fill includes cesium, said cesium being present in quantities of 5.25 X 10 7 to 6.8 X 10 5 gram atoms per centimeter of arc length.
 5. The device of claim 2 wherein said fill includes cesium, said cesium being present in quantities of 5.25 X 10 7 to 6.8 X 10 5 gram atoms per centimeter of arc length.
 6. The device of claim 3 wherein said fill includes cesium, said cesium being present in quantities of 5.25 X 10 7 to 6.8 X 10 5 gram atoms per centimeter of arc length. 